I'm not sure what the article means by "ahead of schedule". The release date was set months ago, and new versions are always released a few days early via the Mozilla FTP servers.
Firefox 5 isn't a huge release, and there won't be nearly as much fanfare as there was with 4. The point of Firefox 5 is to switch over to the "train" model. The train leaves four times a year, no matter what-- and if a feature doesn't make the train, it has to catch the next train. There is no waiting for a feature.
Incrementing by one each release (rather than 4.1, etc) may seem like Mozilla is making a big deal out of nothing, for the sake of publicity. However, it just means that all releases are equal. There will never be a huge 3.6 => 4 style release ever again, and eventually people will lose track of what Firefox version they have (much like how people have lost track of Chrome versions).
tl;dr: While it has a few cool new features, Firefox 5 is more to get Mozilla in the release-often groove.
1. Upgrades will be downloaded in the background and installed automatically by default. It's not yet as seamless as Chrome, though it's moving that direction. (For example, a while after the upgrade is downloaded, current versions of Firefox will prompt you to restart, with a dialog which is a bit more intrusive than the tiny "Christmas tree" toolbar icon that Chrome uses.)
2. Updates will be automatic by default. They'll be installed without prompting, unless users disable auto-updating. This is important because, just like Chrome, the updates will include security fixes.
It's the same release model as Chrome. Chrome doesn't go from 10.1 to 10.2 to 10.3... It's a time boxed release. 4-6 times a year you get an automatic upgrade and the version number is increased. They could have chosen the smaller increment like 10.01, 10.02, ... but then we would never have a major upgrade, and I think humans prefer the major upgrades numbers. In reality, it's just a number. They could have started with 3.14 and added the numbers of Pi, but that's already been done.
The expanding-decimal notation is very appropriate for TeX, because its implementation is just converging to the behavior specified in the TeXbook (i.e., pi), not adding features.
I wish the lesson learned from Chrome was that version numbers don't matter. I think it's unfortunate that some people have drawn the exact opposite conclusion.
Sadly, there isn't much to write about because there isn't anything new here. As far as I can tell, tech blogs don't write about Chrome versions anymore -- I don't even know what number they are up to.
12 is the current release, and 13 should be ready soon. One thing chrome has done really well is smooth and seamless upgrades, this helps them move things forward and people don't notice the version numbers crawl up.
They're going to make four releases a year, so there will never be another major release. Sticking with the old numbering scheme would result in "deflated" version numbers like 4.39.
I feel like everyone saying how we'll have Firefox 346 is missing the point.
The point is really to set up something like a rolling release system where you don't really care which version you are running. The only thing you choose according to your risk appetite is how stable your channel of updates is.
Maybe they'll end up with something like Processing's[1] versioning scheme, where there are fairly regular numbered releases (e.g., release 0115) and some are granted a special status (e.g., release 0196 = version 1.5.1). I suppose it's really just another 'layer' of versioning: VCS commit -> release number -> version number instead of VCS commit -> version number.
I think we'll see a phase out of version numbers on public facing download sites and just have "Firefox" instead of "Firefox v4, v5" etc. Internally, devs might have Firefox 1243053 but we might never see that as the version number, sadly.
Firefox 5 isn't a huge release, and there won't be nearly as much fanfare as there was with 4. The point of Firefox 5 is to switch over to the "train" model. The train leaves four times a year, no matter what-- and if a feature doesn't make the train, it has to catch the next train. There is no waiting for a feature.
Incrementing by one each release (rather than 4.1, etc) may seem like Mozilla is making a big deal out of nothing, for the sake of publicity. However, it just means that all releases are equal. There will never be a huge 3.6 => 4 style release ever again, and eventually people will lose track of what Firefox version they have (much like how people have lost track of Chrome versions).
tl;dr: While it has a few cool new features, Firefox 5 is more to get Mozilla in the release-often groove.